The present invention relates to fabricating multi-perforated parts out of composite material, i.e. parts made of fiber reinforcement densified by a matrix and in which a plurality of perforations have been made.
Multi-perforated parts made out of composite material find particular applications specifically in the fields of filtering and acoustics. For composite material parts having acoustic functions, it is common practice to make perforations therein, as applies for example to the skins of acoustic attenuation panels that are present in aeroengines. In order to enable soundwaves to penetrate into the insides of such panels and be attenuated, the skins of the panels need to present a plurality of perforations.
For parts made out of ceramic matrix composite (CMC) material, the parts need to be made by impregnating a fiber texture that is to form the reinforcement of the part with a resin that is a precursor of a ceramic, by polymerizing the resin, and by proceeding to pyrolize the impregnated texture in order to form a ceramic matrix therein.
Perforations may be made in various ways in a part that is made of CMC material. In particular, they may be made by drilling the impregnated texture while it is in the polymerized stage using a drill bit. Nevertheless, the machining needs to be performed without lubrication in order to avoid degrading the material present in the impregnated texture (chemical incompatibility). That leads to premature wear of the drill bit. In addition, the cutting is not perfect and allows fibrils to appear in the perforations, which fibrils lead to subsequent problems in the fabrication of the part.
The perforations may also be made by using a laser to drill the impregnated texture at the polymerized stage. Under such circumstances, the texture is cut cleanly (no fibrils), but thermally affected zones (TAZ) appear in the texture.
Another solution consists in placing the resin-impregnated texture on a board having surface spikes and then polymerizing the resin. Nevertheless, such tooling is very expensive and sometimes difficult to use.
Composite material parts to which the present invention applies can also be made out of CMC material of the oxide/oxide type, i.e. by depositing refractory oxide particles within a fiber texture made of oxide fibers and then sintering the particles so as to form a refractory oxide matrix in the texture.
The above-mentioned drawbacks of the techniques for making perforations occur likewise when making perforations in a fiber texture containing refractory oxide particles.
Consequently, there exists a need for a solution that makes it possible to make multiple perforations in a composite material part and to do so while complying with the shapes defined for the perforations (no fibrils) and at a production cost that is as low as possible.